1. Field of the Invention
The present invention relates to a rotor for an oil pump that is capable of reducing noise.
2. Description of the Related Art
Many of the conventional oil pumps are internal gear pumps that use trochoidal gears. For the purpose of improving the performances of these pumps, attempts have been made to change the shapes of details of the teeth of the outer rotor and the inner rotor in these pumps. Examples of the improved pumps include the one described in Japanese Patent Application Publication No. 2011-17318 (“Patent Document 1,” hereinafter).
In Patent Document 1, one of the teeth of the inner rotor is constructed with a part of a curve extending along the circumferential axis of the ellipse of the tooth. As shown in FIGS. 6, 7, 8 and the like of Patent Document 1, the angle of each tooth curve of the inner rotor changes suddenly at the inflection point at which the ellipses are connected to each other. Rattling sound occurs when the outer rotor passes the inflection point where the angle suddenly changes. The problem in Patent Document 1, therefore, is this resultant loud noise. An object of the present invention (technical problem that the present invention intends to solve) is to provide a rotor for an oil pump that is capable of reducing noise.